Anisotropic conductive film and method for producing the same

ABSTRACT

An anisotropic conductive film, and its production method, especially suitable for mounting a semiconductor package and sufficiently satisfying the requirements of higher density mounting because short circuit does not occur in the plane direction of the film even if the pitch of electrodes is small, or suitable for mounting a contact probe because conductive connection not fused with a high current can be ensured with a lower pressure and even a high frequency signal can be dealt with. The anisotropic conductive film contains metal powder having such a shape that many fine metal particles are linked as a conductive component, wherein the length of the chain of metal powder is set not longer than the distance between adjacent electrodes being bonded conductively when a semiconductor package is mounted, and the diameter of the chain is set in the range of 1 μm-20 μm when a contact probe is mounted. At least a part of the film is formed while orienting a chain formed of a paramagnetic metal with a magnetic field.

TECHNICAL FIELD

The present invention relates to a new anisotropic conductive film usedfor electronics mounting, and a method of producing the same.

BACKGROUND ART

One of the methods of electronics mounting for mounting a semiconductorpackage on a printed circuit board, or electrically connectingrespective conductor circuits on two printed circuit boards to eachother and coupling or fixing both the printed circuit boards to eachother is a method using a film-shaped anisotropic conductive film (see,Japanese Laid Opened Patent Publication Nos. JP-H06-102523-A2 (1994),JP-H08-115617-A2 (1996), etc.).

When a semiconductor package is mounted, a semiconductor package havinga plurality of bumps arranged on its mounting surface to a printedcircuit board to form a connecting portion, and a printed circuit boardhaving a plurality of electrodes arranged with the same pitch as thepitch of the bumps in its region where the semiconductor package ismounted to form a connecting portion are prepared, and the semiconductorpackage and the printed circuit board are thermally bonded in a statewhere the connecting portions are opposed to each other and ananisotropic conductive film is interposed therebetween while beingaligned with each other such that the bump and the electrode, in each ofpairs, in both the connecting portions are overlapped with each other inthe plane direction of the film.

When printed circuit boards are connected to each other, two printedcircuit boards respectively having pluralities of electrodes arrangedtherein with the same pitch at their connecting positions to formconnecting portions are prepared, and are thermally bonded in a statewhere the connecting portions are opposed to each other and ananisotropic conductive film is interposed therebetween while beingaligned with each other such that the respective electrodes, in each ofpairs, in both the connecting portions are overlapped with each other inthe plane direction of the film.

The anisotropic conductive film generally has a structure in which apowdered conductive component is dispersed in a film havingheat-sensitive adhesive properties including a binding agent such asthermoplastic resin or curable resin.

In the anisotropic conductive film, in order to prevent the occurrenceof such short circuit in the plane direction of the film that the bumpand the electrode or the electrode and the electrode, in each of thepairs, which are arranged with each other in the plane direction of thefilm are short-circuited with the bump and the electrode or theelectrode and the electrode in the adjacent pair, a filling factor,found by the following equation (1), of the conductive component suchthat a conductive resistance in the plane direction (referred to as an“insulating resistance”) is increased: $\begin{matrix}{\text{filling~~factor (vol. \%)} = {\frac{\text{(volume of conductive component)}}{\text{(total volume of solid contents)}} \times 100}} & (1)\end{matrix}$In a case where the film is formed by the conductive component and thebinding agent as solid contents, as described above, the total volume ofthe solid contents in the equation is the total of both the volumes ofthe conductive component and the binding agent.

The anisotropic conductive film is compressed in the thickness directionby heating and pressurization at the time of thermal bonding, so thatthe filling factor of the conductive component in the thicknessdirection is increased, and the conductive components are brought inclose proximity to or into contact with each other to form a conductivenetwork. As a result, a conductive resistance in the thickness direction(referred to as a “connecting resistance”) is reduced. In this case,however, the filling factor of the conductive component in the planedirection of the anisotropic conductive film is not increased.Therefore, the plane direction maintains an initial state where theinsulating resistance is high and the conductivity is low.

Thus, the anisotropic conductive film has anisotropic conductiveproperties in which the connecting resistance in the thickness directionis low and the insulating resistance in the plane direction is high. Theanisotropic conductive film allows,

-   -   while preventing the above-mentioned short circuit in the plane        direction of the film from occurring, to maintain an        electrically independent state for each of the bump-electrode        pairs or the electrode-electrode pairs,    -   the bumps and the electrodes or the electrodes and the        electrodes in all the pairs, which are respectively arranged        with each other in the plane direction of the film, to be        simultaneously conductively connected to each other.

In addition thereto, the heat-sensitive adhesive properties of the filmallows the semiconductor package to be fixed on the printed circuitboard by thermal bonding or the printed circuit boards to be fixed toeach other by thermal bonding.

The use of the anisotropic conductive film makes it easy to perform workfor electronics mounting.

Various types of metal powders such as an Ni powder having an averageparticle diameter of several to several tens of micrometers and having agranular shape, a spherical shape, or a foil shape (a scale shape, aflake shape), resin powder whose surface is gold-plated, and so on areput to practical use as a conductive component included in theconventional anisotropic conductive film.

The conventional anisotropic conductive film generally contains theabove-mentioned metal powder such that the filling factor found in theforegoing equation (1) is 7 to 10% by volume.

In the range of the filling factor, however, the value of the connectingresistance in the thickness direction after thermal bonding is notsufficient, so that the number of cases where it is required that theconnecting resistance should be made much lower is increasing.

Therefore, it is considered that the filling factor of the metal powderserving as a conductive component is made higher than that in theabove-mentioned range in order to further make the connecting resistancein the thickness direction lower than before.

In such a case, however, in the conventional anisotropic conductive filmusing the above-mentioned general metal powder, the insulatingresistance in the plane direction of the film is also reduced, so thatshort circuit in the plane direction of the film easily occurs.

Since such a problem easily occurs, the conventional anisotropicconductive film cannot cope with the above-mentioned requirements unlessthe pitch of the adjacent bumps or electrodes composing the connectingportion is not less than 50 μm. In the present circumstances, theconventional anisotropic conductive film cannot cope with requirementsof higher density mounting in the field of electronics mounting.

In recent years, the inventors have examined that in a probe card usedfor examining whether or not a semiconductor package chip such as amemory, an IC, an LSI (Large Scale Integrated Circuit), or an ASIC(Application Specific Integrated Circuit) is normally manufactured, oneanisotropic conductive film is used in place of a lot of wirings usedfor respectively connecting a lot of fine contact probes mounted on amounting substrate to electrodes provided on a circuit in a probe cardmain body. The inventors have considered that in such connection, themounting pitch of the contact probes is approximately 100 to 200 μm incorrespondence with the pitch of pads in the semiconductor package chipand therefore, even the conventional anisotropic conductive film cancope with the above-mentioned requirements.

That is, the probe card serves to achieve conduction by pressing thecontact probe against the pad on the semiconductor package chip whichhas not been cut to a predetermined size, formed on a wafer, therebyconnecting a circuit in the semiconductor package chip to an externalexamination circuit through the circuit in the probe card main body toexamine the circuit. However, as the semiconductor package chip isminiaturized and highly integrated, the pad itself or the formationpitch thereof is miniaturized, or the number of pads is increased, thecontact probe itself tends to be refined or highly integrated on themounting substrate.

Particularly in recent years, a probe card in which a lot of very finecontact probes processed with a processing accuracy in micron units aremounted on a mounting substrate with the same pitch of 100 to 200 μm asthe pitch of the pads in the semiconductor package chip, as describedabove, has been put to practical use.

In the probe card for examining several tens to several hundreds ofsemiconductor package chips formed on one wafer, however, severalthousands of contact probes must be mounted on the mounting substrate.The number of wirings for connecting the contact probes and the probecard main body must be also the same as the number of contact probes.Therefore, the number of times of soldering of the wirings becomesenormous.

Therefore, the manufacture of the probe card and the management thereofat the time of use are significantly difficult.

Therefore, the inventors have examined that a lot of wirings and theirsoldering are replaced with one anisotropic conductive film. Even if theconventional anisotropic conductive film is simply used for anotherpurpose, however, the following problems occur. Therefore, it has beenfound that practical applications thereof are difficult.

(i) When an internal circuit in a semiconductor package chip to betested is short-circuited, a large current of not less than 1 A, mayflow locally through the anisotropic conductive film at the time of thetest. However, the conventional anisotropic conductive film does notconsider response to such a large current. A current value to be allowedis only several ten milliamperes. When a large current flows by shortcircuit or the like, therefore, Joule heat is produced so that thetemperature of the anisotropic conductive film locally rises. Therefore,the anisotropic conductive film may be fused.

(ii) The contact probe is very small and is liable to be destroyed, asdescribed above. When the anisotropic conductive film is used formounting the contact probe, that is, connection to an electrode,therefore, pressurization at the time of thermal bonding must beperformed at a lower pressure, as compared with that in the case of theabove-mentioned normal connection between the bump and the electrode orbetween the electrodes. When the contact probe and the electrode areconnected to each other at a low pressure, however, a connectingresistance in the thickness direction cannot be reduced to asufficiently practical level, which may cause inferior connection in theconventional anisotropic conductive film.

(iii) When the filling factor of a metal powder is increased in order toeliminate the inferior conduction, the insulating resistance in theplane direction is also reduced in the conventional anisotropicconductive film. Even if the pitch is 100 to 200 μm, the above-mentionedshort circuit in the plane direction of the film, that is, short circuitbetween the contact probe and the electrode, in each of the pairs, whichare arranged with each other in the plane direction of the film in thiscase, and the contact probe and the electrode in the adjacent pair mayoccur.

(iv) In order to examine a semiconductor package chip for a graphicboard or a computer game and a high-speed semiconductor package chipsuch as a Ga—As device, at an operation speed actually used, ahigh-frequency signal must be used. When the filling factor of the metalpowder is increased to eliminate the inferior conduction as in the item(iii), however, it is difficult to pass the high-frequency signalbecause the impedance of the anisotropic conductive film is increased,so that the anisotropic conductive film may be unable to be examined.

(v) The semiconductor package chip to be examined by the probe card isdistributed over the whole surface of one wafer in many cases, asdescribed above. Therefore, the substrate on which the contact probe ismounted and the probe card main body are formed to such large sizes asto cover the wafer. Consequently, the anisotropic conductive film forconnecting the probe card must cover a significantly larger size thanthat for the conventional semiconductor mounting. Moreover, at the timeof the above-mentioned connection at a low pressure, variations in thethickness direction such as warping of the large members must beabsorbed over the whole surface, not to cause inferior connection,inferior conduction, and so on. However, it is difficult for theconventional anisotropic conductive film to cope with such requirements.

DISCLOSURE OF THE INVENTION

A primary object of the present invention is to provide a newanisotropic conductive film capable of sufficiently coping withrequirements of higher density mounting particularly for mounting asemiconductor package or the like because there occurs no short circuitin the plane direction of the film even if the pitch of adjacent bumpsor electrodes composing a connecting portion is less than 50 μm and morepreferably not more than 40 μm.

Another object of the present invention is to provide a new anisotropicconductive film particularly suitable for mounting of a contact probe orthe like because it can make conductive connection more reliably byconnection at a lower pressure than that in the above-mentioned case ofmounting a semiconductor package, is not fused even if a large currentflows, and can also cope with a high-frequency signal.

Still another object of the present invention is to provide a method ofproducing such a new anisotropic conductive film.

An anisotropic conductive film according to the present invention ischaracterized in that a metal powder having the form of a lot of finemetal particles being linked in a chain shape is contained as aconductive component.

The metal powder used as the conductive component in the presentinvention is formed in the form of a lot of fine metal particles on theorder of microns to the order of sub-microns being linked in a chainshape from the beginning by a reduction and deposition method, describedlater. As particularly described later, in a metal powder having astructure in which a metal film is further deposited around a lot ofmetal particles linked to each other, the metal particles are directlyconnected to each other. The increase in contact resistance between themetal particles is restrained, as compared with that in a set ofconventional metal powders in a granular shape or the like, therebyallowing the conductive properties of the metal powder itself to beimproved.

The specific surface area of the above-mentioned chain-shaped metalpowder is larger than that of the conventional metal powder in agranular shape or the like. Accordingly, the metal powders can be alsouniformly dispersed in the binding agent without aggregating.

Moreover, in the chain-shaped metal powder, the ratio of the thicknessto the length of the chain is as high as approximately 10 to 100. Evenif the metal powder is added in a small amount, a network having goodconductive properties can be formed in the anisotropic conductive film.

In the anisotropic conductive film according to the present invention,therefore, the connecting resistance in the thickness direction can bemade significantly lower than before without making the filling factorof the metal powder very high, that is, while maintaining the insulatingresistance in the plane direction of the anisotropic conductive film ata high level.

In a case where the anisotropic conductive film according to the presentinvention is used for mounting a semiconductor package, even if thesemiconductor package is a fine component in which the pitch of adjacentbumps or electrodes composing a connecting portion is less than 50 μmand more preferably not more than 40 μm, conductive connection can bemade reliably without causing short circuit in the plane direction ofthe film, described above, thereby making it possible to sufficientlycope with requirements of higher density mounting.

In a case where the anisotropic conductive film according to the presentinvention is used for mounting a contact probe, a lot of contact probescan be conductively connected more reliably by connection at a lowerpressure without making the filling density of the metal powder veryhigh, as described above, and therefore in a state where the impedanceis maintained at a low level to allow the passage of a high-frequencysignal.

In the present invention, it is preferable that the chain of the metalpowder is oriented in the thickness direction of the film.

When the chain of the metal powder is oriented in the thicknessdirection of the film, the connecting resistance in the thicknessdirection can be more significantly reduced.

It is preferable that the chain-shaped metal powder or each of the metalparticles forming the metal powder is formed of

-   -   a metal having paramagnetism,    -   an alloy of two or more types of metals having paramagnetism,    -   an alloy of a metal having paramagnetism and another metal, or    -   a complex containing a metal having paramagnetism.

In the above-mentioned configuration, if the fine metal particles on theorder of submicrons are deposited by a reduction and deposition method,described later, the metal particles are made magnetic. A lot of metalparticles are linked in a chain shape by a magnetic force so that thechain-shaped metal powder is automatically formed.

Accordingly, the chain-shaped metal powder is easy to produce, therebymaking it possible to improve the production efficiency of theanisotropic conductive film and reduce the cost thereof.

Examples of the metal powder include ones having various structures fromone in which a lot of fine metal particles are linked in a chain shapemerely by a magnetic force, as described above, to one in which a metallayer is further deposited around linked metal particles so that themetal particles are tightly bonded to one another. In either one ofthem, however, the metal particles basically hold a magnetic force.

Therefore, the chain is not easily cut even by the degree of stresscreated in producing the composite material or in applying the compositematerial on a base to form the anisotropic conductive film. Even if thechain is cut, the chain is recombined, at the time point where thestress is not applied. Moreover, in a coating film after theapplication, a plurality of metal powders are brought into contact withone another on the basis of a magnetic force of the metal particles sothat a conductive network is easily formed.

Consequently, the connecting resistance in the thickness direction ofthe anisotropic conductive film can be also made lower.

It is preferable that the whole of the metal powder formed of a metalhaving paramagnetism, an alloy of two or more types of metals havingparamagnetism, or an alloy of a metal having paramagnetism and anothermetal out of the foregoing metal powders or each of the metal particles,or

-   -   a portion, of the metal powder formed of a complex containing        the metal having paramagnetism or each of the metal particles,        containing the metal having paramagnetism,    -   is formed by being deposited in a solution containing a reducing        agent by adding ions forming the metal having paramagnetism        which is its forming material to the solution.

Such a reduction and deposition method allows the chain-shaped metalpowder to be automatically formed, as described above.

The respective particle diameters of the metal particles formed by thereduction and deposition method are uniform, and the particle diameterdistribution is sharp. This is for reduction reaction to uniformlyprogress in a system. Consequently, the metal powder produced from themetal particles is superior in the effect of bringing the connectingresistance in the thickness direction of the anisotropic conductive filmto a uniform state over the whole of the anisotropic conductive film.

It is preferable that a trivalent titanium compound is used as thereducing agent.

When the trivalent titanium compound such as titanium trichloride isused as the reducing agent, the solution obtained after the chain-shapedmetal powder is formed by being deposited can be repeatedly regeneratedto a state where it can be utilized for producing the chain-shaped metalpowder by electrolytic regeneration.

When the anisotropic conductive film according to the present inventionrespectively contains a chain-shaped metal powder and a binding agent assolid contents, it is preferable that the filling factor of the metalpowder found by the foregoing equation (1) is 0.05 to 20% by volume.

In a case where the filling factor is less than 0.05% by volume, theamount of the metal powder that contributes to conduction in thethickness direction of the anisotropic conductive film is too small, sothat the connecting resistance in the same direction after thermalbonding may be unable to be sufficiently reduced. On the other hand,when the filling factor exceeds 20% by volume, the insulating resistancein the plane direction of the anisotropic conductive film is too low sothat short circuit in the plane direction of the film may easily occur.

It is preferable that used as the chain-shaped metal powder is onehaving the form of a lot of fine metal particles being linked in astraight-chain shape or a needle shape.

In a case where the straight-chain-shaped or needle-shaped metal powderis used, the connecting resistance in the thickness direction of theanisotropic conductive film can be further reduced, and the insulatingresistance in the plane direction thereof can be further increased.Particularly in orienting the chain of the metal powder in the thicknessdirection of the film, an interaction between the metal powders arrangedin the direction of orientation can be made stronger, and an interactionbetween the metal powders arranged in the transverse direction crossingthe direction of orientation can be made weaker. Therefore, theabove-mentioned effect produced by using the chain-shaped metal powdercan be more significantly exhibited.

It is preferable that the length of the chain of the metal powder isless than the distance between adjacent electrodes, composing aconnecting portion, conductively connected by using the anisotropicconductive film according to the present invention.

Particularly in a case where a semiconductor package is mounted, whenthe length of the chain of the metal powder is defined to less than thedistance between the adjacent electrodes, as described above, adjacentbumps or electrodes are not short-circuited even if the chain-shapedmetal powder falls sideways at the time of thermal bonding. This allowsthe occurrence of short circuit in the plane direction of the film to bereliably prevented.

It is preferable that in the chain of the metal powder in which thelength of the chain is in the above-mentioned range, the diameter of thechain is not more than 1 μm.

If the diameter of the chain is within the above-mentioned range,particularly in a case where a semiconductor package is mounted, shortcircuit in the plane direction of the film does not occur by the effectof making an interaction between the metal powders strong or weak, asdescribed above, even if the pitch of adjacent bumps or electrodes isless than 50 μm and more preferably not more than 40 μm.

In order to set the diameter of the chain to not more than 1 μm, it ispreferable that the particle diameter of each of the metal particlesforming the chain is not more than 400 nm.

Furthermore, it is preferable that in the above-mentioned metal powder,the ratio L/D of the length L to the diameter D of the chain is not lessthan 3.

In a case where the ratio L/D is less than 3, the length of the chain istoo small, so that the effect of reducing the contact resistance of theanisotropic conductive film without causing short circuit in the planedirection of the film may not be obtained by the effect of making aninteraction between the metal powders strong or weak, as describedabove.

In the mounting of a semiconductor package considering that theconnecting resistance in the thickness direction of the anisotropicconductive film by thermal bonding is made sufficiently low, it ispreferable that the chain-shaped metal powder is formed of a complex ofa chain formed of a metal having paramagnetism, an alloy of two or moretypes of metals having paramagnetism, an alloy of a metal havingparamagnetism and another metal, or a complex containing a metal havingparamagnetism and at least one metal, with which a surface of the chainis coated, selected from a group consisting of Cu, Rb, Rh, Pd, Ag, Re,Pt, and Au.

On the other hand, in the mounting of a contact probe, considering thata large current is caused to flow while preventing short circuit in theplane direction of the film and suppressing the impedance level to a lowlevel to allow the passage of a high-frequency signal, it is preferablethat the diameter of the chain of each of the metal powders is set in arange exceeding 1 μm larger than that in the above-mentioned case, andeach of the chains is oriented in the thickness direction of the filmsuch that there occurs no short circuit in the plane direction of thefilm.

Even if the pitch of the adjacent contact probes or electrodes is 100 to200 μm, as described above, it is preferable that the diameter of thechain of the metal powder is not more than 20 μm in order to package thecontact probes without causing short circuit in the plane direction ofthe film by the effect of making an interaction between the metalpowders strong or weak, as described above.

In the mounting of a contact probe, it is preferable that the fillingfactor of the metal powder is 0.05 to 5% by volume in order to restrainthe rise in impedance to allow the passage of a high-frequency signal.

Furthermore, in the mounting of a contact probe, considering that theconnecting resistance at the time of connection at a low pressure isfurther reduced, it is preferable that the chain-shaped metal powder isformed of a complex of a chain formed of a metal having paramagnetism,an alloy of two or more types of metals having paramagnetism, an alloyof a metal having paramagnetism and another metal, or a complexcontaining a metal having paramagnetism and at least one metal, withwhich a surface of the chain is coated, selected from a group consistingof Cu, Rb, Rh, Pd, Ag, Re, Pt, and Au.

Out of the anisotropic conductive films according to the presentinvention, one in which the chain-shaped metal powder is oriented in thethickness direction of the film can be produced by:

-   -   (1) a method comprising the steps of applying a composite        material, having fluidity, containing a chain-shaped metal        powder formed of a metal at least a part of which has        paramagnetism and a binding agent on a base to which a magnetic        field is applied in a direction crossing a surface of the base,        to orient the chain of the metal powder in the composite        material in the thickness direction of the film along the        direction of the magnetic field, and solidifying or curing the        composite material to fix the orientation of the chain, or    -   (II) a method comprising the steps of spraying a chain-shaped        metal powder formed of a metal at least a part of which has        paramagnetism on a base to which a magnetic field is applied in        a direction crossing a surface of the base, to orient the chain        of the metal powder in the direction of the magnetic field, and        applying thereon a coating agent, having fluidity, containing a        binding agent, and solidifying or curing the coating agent to        fix the orientation of the chain.

According to the producing methods, the anisotropic conductive film inwhich the chain of the metal powder is oriented in the thicknessdirection of the film can be produced more efficiently.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1F are cross-sectional views each showing an example of achain-shaped metal powder contained as a conductive paste in ananisotropic conductive film according to the present invention inpartially enlarged fashion.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described.

An anisotropic conductive film according to the present invention ischaracterized in that it contains a metal powder having the form of alot of fine metal particles being linked in a chain shape as aconductive component.

(Metal Powder)

Usable as the chain-shaped metal powder is any of various metal powdersrespectively produced by various types of methods such as a vapor phasemethod and a liquid phase method and having chain structures. It ispreferable that a lot of fine metal particles are connected to oneanother in a straight-chain shape or a needle shape.

It is preferable that as the chain-shaped metal powder, the metal powderor each of the metal particles forming the metal powder is formed of ametal having paramagnetism, an alloy of two or more types of metalshaving paramagnetism, an alloy of a metal having paramagnetism andanother metal, or a complex containing a metal having paramagnetism.

Specific examples of the metal powder containing the metal havingparamagnetism include any one of the following types of metal powders(a) to (f) or a mixture of two or more types of metal powders.

(a) A metal powder M1 obtained by linking a lot of metal particles m1 onthe order of sub-microns, formed of a metal having paramagnetism, analloy of two or more types of metals having paramagnetism, or an alloyof a metal having paramagnetism and another metal, in a chain shape byits own magnetism, as illustrated in partially enlarged fashion in FIG.1A.

(b) A metal powder M2 obtained by further depositing a metal layer m2composed of a metal having paramagnetism, an alloy of two or more typesof metals having paramagnetism, or an alloy of a metal havingparamagnetism and another metal on a surface of the metal powder M1 inthe foregoing item (a), to tightly bond metal particles to one another,as illustrated in partially enlarged fashion in FIG. 1B.

(c) A metal powder M3 obtained by further depositing a metal layer m3composed of the other metal such as Ag, Cu, Al, Au, or Rh or an alloy onthe surface of the metal powder M1 in the foregoing item (a), to tightlybond metal particles to one another, as illustrated in partiallyenlarged fashion in FIG. 1C.

(d) A metal powder M4 obtained by further depositing a metal layer m4composed of the other metal such as Ag, Cu, Al, Au, or Rh or an alloy ona surface of the metal powder M2 in the foregoing item (b), to tightlybond the metal particles to one another, as illustrated in partiallyenlarged fashion in FIG. 1D.

(e) A metal powder M5 obtained by coating a surface of a granular corematerial m5 a formed of a metal having paramagnetism, an alloy of two ormore types of metals having paramagnetism, or an alloy of a metal havingparamagnetism and another metal with a coating layer m5 b composed ofthe other metal such as Ag, Cu, Al, Au, or Rh or an alloy to obtain acomplex m5, and linking a lot of complexes m5 in a chain shape as metalparticles by the magnetism of the core material m5 a, as illustrated inpartially enlarged fashion in FIG. 1E.

(f) A metal powder M6 obtained by further depositing a metal layer m6composed of the other metal such as Ag, Cu, Al, Au, or Rh or an alloy ona surface of the metal powder M5 in the foregoing item (e), to tightlybond the metal particles to one another, as illustrated in partiallyenlarged fashion in FIG. 1F.

Although in the drawings, the metal layers m2, m3, m4, and m6 and thecoating layer m5 are respectively described as single layers, each ofthe layers may have a laminated structure of two or more layers composedof the same metal material or different metal materials.

It is preferable that

-   -   the whole of the metal powder formed of a metal having        paramagnetism, an alloy of two or more types of metals having        paramagnetism, or an alloy of a metal having paramagnetism and        another metal out of the foregoing metal powders or each of the        metal particles, or    -   a portion, of the metal powder or each of the metal particles        formed of a complex containing a metal having paramagnetism,        containing the metal having paramagnetism,    -   is formed by being deposited in a solution containing ions        forming a metal having paramagnetism which is its forming        material by adding a reducing agent to the solution by the        reduction and deposition method.

In the reduction and deposition method, ammonia water or the like isadded to a solution in which a trivalent titanium compound such astitanium trichloride serving as a reducing agent and sodium citrate orthe like, are dissolved (hereinafter referred to as a “reducing agentsolution”) to adjust the pH thereof to 9 to 10. Consequently, trivalenttitanium ions are bonded to a citric acid serving as a complexing agentto form a coordination compound, so that activation energy in the caseof oxidation from Ti (III) to Ti (IV) is lowered, and a reductionpotential is raised. Specifically, a potential difference between Ti(III) and Ti (IV) exceeds 1 V. This value is a significantly highervalue, as compared with a reduction potential from Ni (II) to Ni (0) anda reduction potential from Fe (II) to Fe (0). Accordingly, it ispossible to efficiently reduce ions forming various types of metals, todeposit and form metal particles, metal films, and so on.

A solution containing ions forming a metal having paramagnetism such asNi or a solution containing two or more types of ions forming an alloycontaining a metal having paramagnetism is then added to theabove-mentioned reducing agent solution.

Consequently, Ti (III) functions as a reducing agent, to reduce metalions and deposit the reduced metal in the solution when itself isoxidized to Ti (IV). That is, metal particles composed of theabove-mentioned metal or alloy are deposited in the solution, and a lotof metal particles are linked in a chain shape by their own magnetism,to form a chain-shaped metal powder. When the deposition is furthercontinued after that, a metal layer is further deposited on a surface ofthe metal powder, thereby tightly bonding the metal particles.

That is, the metal powders M1 and M2 in the foregoing items (a) and (b)and the metal particles m1 which are the original form of the metalpowders, the core materials m5 a in the complexes m5 which are theoriginal form of the metal powders M5 and M6 in the foregoing items (e)and (f), and so on can be produced by the above-mentioned method.

The respective particle diameters of the metal particles m1 or the corematerials m5 a are uniform, and the particle diameter distribution issharp. The reason for this is that reduction reaction uniformlyprogresses in the reaction system. Consequently, any of the metalpowders M1 to M6 produced from the metal particles m1 or the corematerials m5 a is superior in the effect of bringing the conductiveresistance in the thickness direction of the anisotropic conductive filminto a uniform state over the whole surface of the anisotropicconductive film.

The reducing agent solution obtained after the metal particles, the corematerials, or the like are deposited can be utilized for producing thechain-shaped metal powder by the reduction and deposition methodrepeatedly any number of times by performing electrolytic regeneration.That is, if the reducing agent solution obtained after the metalparticles, the core materials, or the like are deposited is put in anelectrolytic cell to reduce Ti (IV) to Ti (III) by applying a voltage,it can be employed as a reducing agent solution for electrolyticdeposition again. This is because titanium ions are hardly consumed atthe time of electrolytic deposition, that is, titanium ions, togetherwith a metal to be deposited, are not deposited.

Examples of a metal or an alloy having paramagnetism forming the metalparticles, the core materials, or the like include Ni, Fe, Co, and analloy of two or more types of the metals. Particularly, Ni, a Ni—Fealloy (Permalloy), and so on are preferable. Particularly metalparticles formed of such a metal or alloy are strong in magneticinteraction in a case where they are linked in a chain shape andtherefore, are superior in the effect of reducing contact resistancebetween the metal particles.

Examples of other metals, together with the above-mentioned metal oralloy having paramagnetism, forming the complexes in the foregoing items(c), (d), (e), and (f) include at least one type of metal selected froma group consisting of Cu, Rb, Rh, Pd, Ag, Re, Pt, and Au, and its alloy.When consideration is given to improvement in the conductive propertiesof the metal powder, it is preferable that a portion formed of the metalor metals is a portion exposed to an outer surface of the chain, asdescribed in the foregoing items (c) to (f). A coating can be formed byvarious types of film forming methods such as an electroless platingmethod, an electroplating method, a reduction and deposition method, anda vacuum deposition method.

Preferable as a metal powder used for mounting a semiconductor packageis one which has the structure as described in any of the foregoingitems (a) to (f) and in which the length of the chain is less than thedistance between adjacent electrodes, composing a connecting portion,conductively connected by using an anisotropic conductive film.

Preferable as the above-mentioned metal powder is one in which thediameter of its chain is not more than 1 μm, and the particle diameterof each of the metal particles forming the chain-shaped metal powder isnot more than 400 nm.

The reason for this is as described above.

It is preferable that the length of the chain is not more than 0.9 timesthe distance between the adjacent electrodes, considering that shortcircuit occurring because the metal powder falls sideways is morereliably prevented.

If the diameter of the chain is too small, the chain is liable to beeasily cut by the degree of stress in a case where the metal powder ismixed with a binding agent or a solvent to prepare a composite materialor in a case where the composite material is applied over a base toproduce an anisotropic conductive film. Therefore, the diameter of thechain is preferably not less than 10 nm.

If the particle diameter of metal particles forming the chain is toosmall, the size of the metal powder itself linked in a chain shape istoo small, so that a function as a conductive component cannot besufficiently obtained. Therefore, it is preferable that the particlediameter of the metal particles is not less than 10 nm.

Furthermore, the lower limit of the length of the above-mentioned chainis not particularly limited. However, it is preferable that the length Lof the chain is set such that the ratio L/D of the length L to thediameter D of the chain is not less than 3 within a range of the mostsuitable diameter of the chain, described above.

If the ratio L/D is less than 3, the shape of the chain comes closer toa granular shape than to a chain shape, so that the effect of loweringthe contact resistance of the anisotropic conductive film withoutcausing short circuit in the plane direction of the film may not beobtained by the effect of making the interaction between the metalpowders strong or weak, as also previously described.

A metal powder having a composite structure in which a surface of itschain is coated with at least one metal selected from a group consistingof Cu, Rb, Rh, Pd, Ag, Re, Pt, and Au, as described in the foregoingitems (c) to (f), is preferable because the conductive propertiesthereof can be improved.

On the other hand, preferable as the metal powder used for mounting acontact probe is one which has a structure described in any of the items(a) to (f) and in which the diameter of its chain exceeds 1 μm and isnot more than 20 μm.

It is preferable that the particle diameter of each of the metalparticles forming the above-mentioned metal powder is 0.5 to 2 μm.

Particularly, a metal powder having a composite structure in which asurface of its chain is coated with at least one metal selected from agroup consisting of Cu, Rb, Rh, Pd, Ag, Re, Pt, and Au, as described inthe foregoing items (c) to (f), is preferable because the conductiveproperties thereof can be improved.

Also usable as the metal powder used for mounting a contact probe is onewhich has the form of a lot of chains having a smaller diameter and ofthe same degree as that used for mounting a semiconductor packageaggregating in a bundle shape and in which the diameter of a chainobtained by the aggregation exceeds 1 μm and is not more than 20 μm.When consideration is given to improvement in conductive properties, asurface of such an aggregate may be coated with the above-mentionedmetal.

There is an anisotropic conductive film having columnar Cu powdershaving a diameter of approximately 20 μm and a length of approximately120 μm being dispersed in resin, which is similar in size to theabove-mentioned metal powder.

When the anisotropic conductive film is used for mounting a contactprobe, however, the conductive properties in the thickness direction ofthe film are insufficient, as apparent from the results in thecomparative examples, described later. It is considered that the reasonfor this is that the metal powder cannot be magnetically oriented in thethickness direction of the film because it is a copper powder. That is,the copper powder cannot be oriented in the thickness direction of thefilm by application of a magnetic field, so that the copper powder isdirected at random by stress at the time of film formation. Therefore, asufficient conductive network cannot be formed in connection at a lowpressure at the time of mounting a contact probe, so that the connectingresistance in the same direction cannot be sufficiently reduced.

(Binding Agent)

Usable as a binding agent, together with a chain-shaped metal powder,forming an anisotropic conductive film is any of various types ofcompounds conventionally known as a binding agent in the use and havingfilm formation properties and adhesive properties. Examples of such abinding agent include thermoplastic resin, curable resin, and liquidcurable resin. Particularly preferable examples include acrylic resin,epoxy resin, fluorocarbon resin, and phenolic resin.

(Composite Material)

A composite metal forming the basis of an anisotropic conductive film isproduced by blending the chain-shaped metal powder and the bindingagent, together with a suitable solvent, in a predetermined ratio.Further, the solvent may be omitted by using a liquid binding agent suchas liquid curable resin.

(Anisotropic Conductive Film and Method of Producing the Same)

An anisotropic conductive film according to the present invention can beproduced by applying the above-mentioned composite material over a basesuch as a glass plate, and drying or solidifying the composite material,or semi-curing, when a binding agent is curable resin or liquid curableresin, the composite material, and then stripping the composite materialfrom the base.

When the anisotropic conductive film is used for mounting asemiconductor package, the thickness of the anisotropic conductive filmis preferably 10 μm to 100 μm, considering that an electrode and a bumpare conductively bonded to each other satisfactorily when they arepressed against each other through the anisotropic conductive film.

When the anisotropic conductive film is used for mounting a contactprobe, the thickness of the anisotropic conductive film is preferably100 μm to 300 μm, considering that variations in the thickness directionby warping or the like of a mounting substrate or a probe card main bodyare absorbed over the whole surface thereof, not to cause inferiorconnection, inferior conduction, or the like.

In the anisotropic conductive film according to the present invention,it is preferable that the chain of the metal powder is fixed in a statewhere it is oriented in the thickness direction of the film in either ofthe uses. Such an anisotropic conductive film can be produced by:

-   -   (A) applying a composite material, having fluidity, containing a        chain-shaped metal powder formed of a metal at least a part of        which has paramagnetism and a binding agent, described above,        over a base to which a magnetic field is applied in a direction        crossing a surface of the base, to solidify or cure the        composite material in a state where the chain of the metal        powder is oriented in the thickness direction of the film along        the direction of the magnetic field to fix the orientation of        the chain of the metal powder, or    -   (B) spraying a chain-shaped metal powder, described above, on a        base to which a magnetic field is applied in a direction        crossing a surface of the base, and applying a coating agent,        having fluidity, including a binding agent in a state where a        chain of the metal powder is oriented in the direction of the        magnetic field, to solidify or cure the coating agent to fix the        orientation of the chain of the metal powder, followed by        stripping from the base.

It is preferable that the strength of the magnetic field applied incarrying out the methods is not less than 1000 μT, not less than 10000μT among them, and particularly not less than 40000 μT in terms of amagnetic flux density, considering that the metal powder in theanisotropic conductive film is sufficiently oriented in the thicknessdirection of the film, although it differs depending on the type, theratio, and so on of the metal having paramagnetism included in the metalpowder.

Examples of a method of applying a magnetic field include a method ofarranging magnets on and under a base such as a glass substrate and amethod utilizing a surface of a magnet as a base. The latter methodutilizes the fact that a magnetic line of force extending from thesurface of the magnet is approximately perpendicular to the surface ofthe magnet in a region from the surface to the degree of the thicknessof the anisotropic conductive film and has the advantage that a devicefor producing the anisotropic conductive film can be simplified.

It is preferable that the filling factor of the metal powder found inthe foregoing equation (1) in the anisotropic conductive film thusproduced is 0.05 to 20% by volume.

Particularly when the anisotropic conductive film is used for mounting acontact probe, it is preferable that the filling factor of the metalpowder is 0.05 to 5% by volume particularly in the above-mentioned rangein order to restrain the rise in impedance to allow the passage of ahigh-frequency signal.

In order to adjust the filling factor in the above-mentioned range, whenthe chain-shaped metal power is not oriented, and in the case describedin the foregoing method (A), the anisotropic conductive film may beformed using a composite material containing the metal powder and thebinding agent in the above-mentioned ratio. On the other hand, in thecase as described in the foregoing method (B), the amount of spraying ofthe metal powder, the concentration of the binding agent in the coatingagent, the amount of application, and so on may be adjusted.

In the anisotropic conductive film according to the present invention,there occurs no short circuit in the plane direction of the film even ifthe pitch of the adjacent electrodes is less than 50 μm and morepreferably not more than 40 μm in the mounting of a semiconductorpackage by the function of the chain-shaped metal powder serving as aconductive component. Therefore, it is possible to sufficiently copewith requirements of higher density mounting in the field of electronicsmounting.

When the anisotropic conductive film is used for mounting a contactprobe, conductive connection can be made more reliably by connection ata lower pressure than that in a case where a semiconductor package ismounted particularly by increasing the diameter of the chain as well asorienting the chain in the thickness direction of the film. Moreover,even if a large current flows, the anisotropic conductive film is notfused, and can cope with a high-frequency signal.

The anisotropic conductive film according to the present invention isalso used for pin mounting in an IC socket in addition to theabove-mentioned uses. Further, it can be also currently employed for athree-dimensional package which is wire-bonded or μ BGA (μ ball gridarray) connected.

Industrial Applicability

As described in the foregoing, the anisotropic conductive film accordingto the present invention can sufficiently cope with requirements ofhigher density mounting particularly for mounting a semiconductorpackage or the like because there occurs no short circuit in the planedirection of the film even if the pitch of adjacent electrodes is madesmaller than that in the present circumstances. Another anisotropicconductive film according to the present invention is suitableparticularly for mounting a contact probe or the like because conductiveconnection can be made more reliably by connection at a lower pressurethan that in the above-mentioned case of mounting a semiconductorpackage and is not fused even if a large current flows therethrough, andcan also cope with a high-frequency signal. Furthermore, a method ofproducing the anisotropic conductive film according to the presentinvention is suited to produce the above-mentioned anisotropicconductive film.

EXAMPLES

The present invention will be described on the basis examples andcomparative examples.

[Anisotropic Conductive Film for Mounting Semiconductor Package]

Example 1

Used as a conductive component was an Ni powder, which has the form offine Ni particles being linked in a straight-chain shape and in whichthe particle diameter of the Ni particles is 100 nm, the diameter D andthe length L of the chain are respectively 400 nm and 5 μm, and theratio L/D is 12.5.

The Ni powder and acrylic resin serving as a binding agent were mixedsuch that the filling factor of the Ni powder found in the foregoingequation (1) would be 20% by volume, and methyl ethyl ketone was addedto a mixture, to prepare a paste-shaped composite material.

The composite material was then applied over a glass substrate, wasdried or solidified, and was then stripped, to produce an anisotropicconductive film having a thickness of 30 μm.

Example 2

An anisotropic conductive film having a thickness of 30 μm was producedin the same manner as that in the example 1 except that an Ni powder,which has the form of fine Ni particles being linked in a straight-chainshape and in which the particle diameter of the Ni particles is 400 nm,the diameter D and the length L of the chain are respectively 1 μm and 5μm, and the ratio L/D is 5, was used as a conductive component, the Nipowder and acrylic resin serving as a binding agent were mixed such thatthe filling factor of the Ni powder would be 0.05% by volume, and methylethyl ketone was added to a mixture, to prepare a paste-shaped compositematerial.

Example 3

An anisotropic conductive film having a thickness of 30 μm was producedin the same manner as that in the example 1 except that a metal powderhaving a composite structure in which a surface of an Ni powder, whichhas the form of fine Ni particles being linked in a straight-chain shapeand in which the particle diameter of the Ni particles is 300 nm, thediameter D and the length L of the chain are respectively 600 nm and 5μm, and the ratio L/D is 8.3, is coated with Ag having a thickness of 50nm was used, and the metal powder and acrylic resin serving as a bindingagent were mixed such that the filling factor of the metal powder wouldbe 1% by volume, and methyl ethyl ketone was added to a mixture, toprepare a paste-shaped composite material.

Example 4

The same composite material as that prepared in the foregoing example 3was applied over a magnet serving as a base, was dried or solidified ina magnetic field with a magnetic flux density of 40000 μT and therefore,was fixed in a state where a metal powder was oriented in the thicknessdirection of the film, followed by stripping, to produce an anisotropicconductive film having a thickness of 30 μm.

Example 5

The same metal powder as that used in the example 3 was sprayed on thesame magnet as that used in the example 4, and was oriented in thethickness direction of the film in a magnetic field with a magnetic fluxdensity of 40000 μT.

In this state, a coating agent obtained by dissolving acrylic resinserving as a binding agent in methyl ethyl ketone was then applied. Theamount of the application was adjusted such that the filling factor ofthe metal powder would be 1% by volume.

The coating agent was dried or solidified and therefore, was fixed in astate where the metal powder was oriented in the thickness direction ofthe film, followed by stripping, to produce an anisotropic conductivefilm having a thickness of 30 μm.

Comparative Example 1

An anisotropic conductive film having a thickness of 30 μm was producedin the same manner as that in the example 1 except that a flake-shapedNi powder with a particle diameter distribution from 5 μm to 20 μm wasused, the Ni powder and acrylic resin serving as a binding agent weremixed such that the filling factor of the Ni powder would be 20% byvolume, and methyl ethyl ketone was added to a mixture, to prepare apaste-shaped composite material.

Comparative Example 2

An anisotropic conductive film having a thickness of 30 μm was producedin the same manner as that in the example 1 except that a sphericalmetal powder having a composite structure in which a surface ofspherical resin particles having a diameter of 5 μm is coated with Auhaving a thickness of 100 nm was used as a conductive component, themetal powder and acrylic resin serving as a binding agent were mixedsuch that the filling factor of the metal powder would be 20% by volume,and methyl ethyl ketone was added to a mixture, to prepare apaste-shaped composite material.

Comparative Example 3

An anisotropic conductive film having a thickness of 30 μm was producedin the same manner as that in the comparative example 2 except that thesame metal powder as that used in the comparative example 2 and acrylicresin serving as a binding agent were mixed such that the filling factorof the metal powder would be 1% by volume, and methyl ethyl ketone wasadded to a mixture, to prepare a paste-shaped composite material.

Measurement of Connecting Resistance

The anisotropic conductive film produced in each of the examples and thecomparative examples was affixed, on a flexible printed circuit board(FPC) having an electrode pattern in which Au electrodes having a widthof 15 μm, a length of 50 μm, and a thickness of 2 μm are arranged at 15μm spacing, to the electrode pattern.

A glass substrate having an Al film deposited on its one surface wasthen thermally bonded upon being pressed at a pressure of 10 g perelectrode while being heated to 100° C. in a state where it wassuperimposed on the anisotropic conductive film such that the Al filmwould be brought into contact therewith.

A resistance value between the two adjacent Au electrodes which areconductively connected to each other through the anisotropic conductivefilm and the Al film was measured, and the measured resistance value wasreduced by half to be a connecting resistance in the thickness directionof the anisotropic conductive film.

The results are shown in Table 1. Evaluations in Table 1 arerespectively as follows:

⊚: The connecting resistance is not more than 0.1 Ω. The conductiveproperties in the thickness direction are significantly good.

◯: The connecting resistance exceeds 0.1 Ω and is not more than 1 Ω. Theconductive properties in the thickness direction are good.

X: The connecting resistance exceeds 1 Ω. The conductive properties inthe thickness direction are bad.

Measurement of Insulating Resistance

The anisotropic conductive film produced in each of the examples and thecomparative examples was affixed to the electrode pattern on the sameFPC as that used in the foregoing.

A glass substrate having no Al film deposited thereon at this time wasthen thermally bonded upon being pressed at a pressure of 10 g perelectrode while being heated to 100° C. in a state where it wassuperimposed on the anisotropic conductive film.

A resistance value between the two adjacent Au electrodes to which theglass substrate was thermally bonded through the anisotropic conductivefilm was measured to be an insulating resistance in the plane directionof the anisotropic conductive film.

The results are shown in Table 1. Evaluations in Table 1 arerespectively as follows:

⊚: The insulating resistance exceeds 1 GΩ. The insulating properties inthe plane direction are significantly good.

◯: The insulating resistance exceeds 1 MΩ and is not more than 1 GΩ. Theinsulating properties in the plane direction are good.

X: The insulating resistance is not more than 1 MΩ. The insulatingproperties in the plane direction are bad. TABLE 1 Connecting Insulatingresistance resistance measured measured value value (evaluation)(evaluation) Example 1   1 Ω(◯)  10 MΩ(◯) Example 2  0.5 Ω(◯)  10 GΩ(⊚)Example 3  0.1 Ω(⊚)  1 GΩ(◯) Example 4 0.05 Ω(⊚)  1 GΩ(◯) Example 5 0.05Ω(⊚)  1 GΩ(◯) Comparative   1 Ω(◯) 100 Ω(X) Example 1 Comparative   1Ω(◯)  1 KΩ(X) Example 2 Comparative   10 KΩ(X)  1 GΩ(◯) Example 3

From Table 1, it was found that both the anisotropic conductive film inthe comparative example 1 in which the flake-shaped Ni powder wascontained at a filling factor of 20% by volume and the anisotropicconductive film in the comparative example 2 in which the sphericalmetal powder having a composite structure of the resin particles and theAu coating was contained at a filling factor of 20% by volume were lowin insulating resistance and were inferior in insulating properties inthe plane direction of the film. Further, it was found that theanisotropic conductive film in the comparative example 3 in which thefilling factor of the spherical metal powder having the above-mentionedcomposite structure was decreased to 1% by volume was high in connectingresistance and was inferior in conductive properties in the thicknessdirection of the film.

On the other hand, it was found that all of the anisotropic conductivefilms in the examples 1 to 5 were low in connecting resistance, weresuperior in conductive properties in the thickness direction of thefilm, were high in insulating resistance, and were superior ininsulating properties in the plane direction of the film.

From the examples 1 and 2, it was confirmed that in order to make theconnecting resistance lower and make the insulating resistance higher,the filling factor of the metal powder in a straight-chain shape mightbe made lower while making the diameter of the chain of the metal powderlarger.

It was confirmed that the surface of the chain of the metal powder mightbe coated with a metal superior in conductive properties in order tofurther reduce the connecting resistance from the examples 1 to 3, andthe chain of the metal powder might be oriented in the thicknessdirection of the film from the examples 3 to 5.

Example 6

Used as a conductive component, an Ni powder, which has the form of fineNi particles being linked in a straight-chain shape and in which theparticle diameter of the Ni particles is 400 nm, the diameter D and thelength L of the chain are respectively 1 μm and 9 μm, and the ratio L/Dis 9.

The Ni powder and acrylic resin serving as a binding agent were mixedsuch that the filling factor of the Ni powder would be 1% by volume, andmethyl ethyl ketone was added to a mixture, to prepare a paste-shapedcomposite material.

The composite material was then applied over a magnet serving as a base,was dried or solidified in a magnetic field with a magnetic flux densityof 200000 μT and therefore, was fixed in a state where the metal powderwas arranged in the thickness direction of the film, followed bystripping, to produce an anisotropic conductive film having a thicknessof 20 μm.

Example 7

An anisotropic conductive film having a thickness of 20 μm was producedin the same manner as that in the example 6 except that an Ni powder,which has the form of fine Ni particles being linked in a straight-chainshape and in which the particle diameter of the Ni particles is 400 nm,the diameter D and the length L of the chain are respectively 3 μm and 9μm, and the ratio L/D is 3, was used as a conductive component.

Comparative Example 4

An anisotropic conductive film having a thickness of 20 μm was producedin the same manner as that in the example 6 except that an Ni powder,which has the form of fine Ni particles being linked in a straight-chainshape and in which the particle diameter of the Ni particles is 400 nm,the diameter D and the length L of the chain are respectively 1 μm and15 μm, and the ratio L/D is 15, was used as a conductive component.

Comparative Example 5

An anisotropic conductive film having a thickness of 20 μm was producedin the same manner as that in the example 6 except that a granular Nipowder, which is composed of an aggregate of fine Ni particles and inwhich the particle diameter of the Ni particles is 400 nm, the minordiameter D and the major diameter L are respectively 6 μm and 9 μm, andthe ratio L/D is 1.5, was used as a conductive component.

Measurement of Connecting Resistance

The anisotropic conductive film produced in each of the examples and thecomparative examples was affixed, on an FPC having an electrode patternin which Au electrodes having a width of 15 μm, a length of 50 μm, and athickness of 5 μm are arranged at 10 μm spacing, to the electrodepattern.

A glass substrate having an Al film deposited on its one surface wasthen thermally bonded upon being pressed at a pressure of 10 g perelectrode while being heated to 100° C. in a state where it wassuperimposed on the anisotropic conductive film such that the Al filmwould be brought into contact therewith.

A resistance value between the two adjacent Au electrodes which areconductively connected to each other through the anisotropic conductivefilm and the Al film was measured, and the measured resistance value wasreduced by half to be a connecting resistance in the thickness directionof the anisotropic conductive film.

The results are shown in Table 2. Evaluations in Table 2 arerespectively as follows:

⊚: The connecting resistance is not more than 0.1 Ω. The conductiveproperties in the thickness direction are significantly good.

◯: The connecting resistance exceeds 0.1 Ω and is not more than 1 Ω. Theconductive properties in the thickness direction are good.

X: The connecting resistance exceeds 1 Ω. The conductive properties inthe thickness direction are bad.

Measurement of Insulating Resistance

The anisotropic conductive film produced in each of the examples and thecomparative examples was affixed to the electrode pattern on the sameFPC as that used in the foregoing.

A glass substrate having no Al film deposited thereon at this time wasthermally bonded upon being pressed at a pressure of 10 g per electrodewhile being heated to 100° C. in a state where it was superimposed onthe anisotropic conductive film.

A resistance value between the two adjacent Au electrodes to which theglass substrate was thermally bonded through the anisotropic conductivefilm was measured to be an insulating resistance in the plane directionof the anisotropic conductive film.

The results are shown in Table 2. Evaluations in Table 2 arerespectively as follows:

⊚: The insulating resistance exceeds 1 GΩ. The insulating properties inthe plane direction are significantly good.

◯: The insulating resistance exceeds 1 MΩ and is not more than 1 GΩ. Theinsulating properties in the plane direction are good.

X: The insulating resistance is not more than 1 MΩ. The insulatingproperties in the plane direction are bad. TABLE 2 Connecting Insulatingresistance resistance measured measured value value (evaluation)(evaluation) Example 6 0.5 Ω(◯)  10 GΩ(⊚) Example 7   1 Ω(◯)  15 GΩ(⊚)Comparative 0.8 Ω(◯) 100 Ω(X) Example 4 Comparative 2.5 Ω(X)  20 GΩ(⊚)Example 5

From Table 2, it was found that the anisotropic conductive film in thecomparative example 4 in which the chain-shaped Ni powder, in which thelength of the chain is larger than the distance between the adjacentelectrodes, is contained was low in insulating resistance and wasinferior in insulating properties in the plane direction of the film. Itwas predicted as this cause that the Ni powder fell sideways at the timeof thermal bonding to cause short circuit between the adjacentelectrodes.

Furthermore, it was found that the anisotropic conductive film in thecomparative example 5 containing the Ni powder having not a chain shapebut a granular shape because the ratio L/D is too low was high inconnecting resistance and was low in conductive properties in thethickness direction of the film.

On the other hand, it was found that both the anisotropic conductivefilms in the examples 6 and 7 were low in connecting resistance and weresuperior in conductive properties in the thickness direction of thefilm, and were high in insulating resistance and were superior ininsulating properties in the plane direction of the film. This provedthat even if the Ni powder fell sideways at the time of thermal bonding,short circuit between the adjacent electrodes could be reliablyprevented by setting the length of the chain to less than the distancebetween the adjacent electrodes.

[Anisotropic Conductive Film for Mounting Contact Probe]

Example 8

Used as a conductive component was an Ni powder, which has the form of aplurality of chains, each having fine Ni particles linked in astraight-chain shape, aggregating in a bundle shape and in which theparticle diameter of the Ni particles is 100 nm, and the diameter andthe length of the chain are respectively 10 μm and 50 μm.

The Ni powder and acrylic resin serving as a binding agent were mixedsuch that the filling factor of the Ni powder would be 1% by volume, andmethyl ethyl ketone was added to a mixture, to prepare a paste-shapedcomposite material.

The composite material was then applied over a magnet serving as a base,was dried or solidified in a magnetic field with a magnetic flux densityof 200000 μT and therefore, was fixed in a state where the metal powderwas oriented in the thickness direction of the film, followed bystripping, to produce an anisotropic conductive film having a thicknessof 120 μm.

Example 9

An anisotropic conductive film having a thickness of 120 μm was producedin the same manner as that in the example 8 except that an Ni powder,which has the form of fine Ni particles being linked in a straight-chainshape and in which the particle diameter of the Ni particles is 1 μm,and the diameter and the length of the chain are respectively 10 μm and50 μm, was used as a conductive component.

Example 10

An anisotropic conductive film having a thickness of 120 μm was producedin the same manner as that in the example 8 except that a metal powderhaving a composite structure in which a surface of an Ni powder, whichhas the form of fine Ni particles being linked in a straight-chain shapeand in which the particle diameter of the Ni particles is 1 μm, and thediameter and the length of the chain are respectively 10 μm and 50 μm,is coated with Ag having a thickness of 50 nm was used as a conductivecomponent.

Example 11

An anisotropic conductive film having a thickness of 120 μm was producedin the same manner as that in the example 8 except that an Ni powder,which has the form of fine Ni particles being linked in a straight-chainshape and in which the particle diameter of the Ni particles is 300 nm,and the diameter and the length of the chain are respectively 600 nm and50 μm, was used as a conductive component.

Comparative Example 6

A spherical Ni powder having a diameter of 5 μm was used as a conductivecomponent, the Ni power and acrylic resin serving as a binding agentwere mixed such that the filling factor of the Ni powder would be 10% byvolume, and methyl ethyl ketone was added to a mixture, to prepare apaste-shaped composite material.

The composite material was then applied over a glass substrate, wasdried or solidified, and was then stripped, to produce an anisotropicconductive film having a thickness of 120 μm.

Comparative Example 7

A metal powder in which a surface of the same spherical resin particleshaving a diameter of 5 μm as that used in the comparative example 2 iscoated with Au having a thickness of 100 nm was used as a conductivecomponent, the metal powder and acrylic resin serving as a binding agentwere mixed such that the filling factor of the metal particles would be10% by volume, and methyl ethyl ketone was added to a mixture, toprepare a paste-shaped composite material.

The composite material was then applied over a glass substrate, wasdried or solidified, and was then stripped, to produce an anisotropicconductive film having a thickness of 120 μm.

Comparative Example 8

A commercially available anisotropic conductive film having a thicknessof 120 μm, in which columnar Cu powders having a diameter of 20 μm and alength of 120 μm were distributed at 30 μm spacing in resin havinginsulating properties, was used as a comparative example 8.

Measurement of Connecting Resistance

The anisotropic conductive film produced in each of the examples and thecomparative examples was affixed, on an FPC having an electrode patternin which Au electrodes having a width of 100 μm, a length of 50 μm, anda thickness of 2 μm are arranged at 40 μm spacing, to the electrodepattern.

A glass substrate having an Al film deposited on its one surface wasthen thermally bonded upon being pressed at a pressure of lg perelectrode while being heated to 100° C. in a state where it wassuperimposed on the anisotropic conductive film such that the Al filmwould be brought into contact therewith.

A resistance value between the two adjacent Au electrodes which areconductively connected to each other through the anisotropic conductivefilm and the Al film was measured, and the measured resistance value wasreduced by half to be a connecting resistance in the thickness directionof the anisotropic conductive film.

The results are shown in Table 3. Evaluations in Table 3 arerespectively as follows:

⊚: The connecting resistance is not more than 0.1 Ω. The conductiveproperties in the thickness direction are significantly good.

◯: The connecting resistance exceeds 0.1 Ω and is not more than 1 Ω. Theconductive properties in the thickness direction are good.

X: The connecting resistance exceeds 1 Ω. The conductive properties inthe thickness direction are bad.

Measurement of Insulating Resistance

The anisotropic conductive film produced in each of the examples and thecomparative examples was affixed, on an FPC having an electrode patternin which Au electrodes having a width of 100 μm, a length of 50 μm, anda thickness of 2 μm are arranged at 40 μm spacing, to the electrodepattern.

A glass substrate having no Al film deposited thereon at this time wasthen thermally bonded upon being pressed at a pressure of 1 g perelectrode while being heated to 100° C. in a state where it wassuperimposed on the anisotropic conductive film.

A resistance value between the two adjacent Au electrodes to which theglass substrate was thermally bonded through the anisotropic conductivefilm was measured, to be an insulating resistance in the plane directionof the anisotropic conductive film.

The results are shown in Table 3. Evaluations in Table 3 arerespectively as follows:

⊚: The insulating resistance exceeds 10 GΩ. The insulating properties inthe plane direction are significantly good.

◯: The insulating resistance exceeds 100 MΩ and is not more than 10 GΩ.The insulating properties in the plane direction are good.

X: The insulating resistance is not more than 100 MΩ. The insulatingproperties in the plane direction are bad.

Measurement of Limiting Current Amount

The anisotropic conductive film produced in each of the examples and thecomparative examples was affixed, on an FPC having an electrode patternin which Au electrodes having a width of 100 μm, a length of 50 μm, anda thickness of 2 μm are arranged at 40 μm spacing, to the electrodepattern.

A glass substrate having an Al film deposited on its one surface wasthen thermally bonded upon being pressed at a pressure of 1 g perelectrode while being heated to 100° C. in a state where it wassuperimposed on the anisotropic conductive film such that the Al filmwould be brought into contact therewith.

When a current was caused to flow between the two adjacent Au electrodeswhich are conductively connected to each other through the anisotropicconductive film and the Al film, and its current value was graduallyincreased, a current value at which disconnection due to fusing occurswas found as a limiting current amount.

The results are shown in Table 3. Evaluations in Table 3 arerespectively as follows:

⊚: The limiting current amount exceeds 1.5 A. The current resistance issignificantly good.

◯: The limiting current value is not less than 1.0 A and is not morethan 1.5 A. The current resistance is good.

X: The limiting current value is less than 1.0 A. The current resistanceis bad. TABLE 3 Connecting Insulating Limiting resistance resistancecurrent measured measured measured value value value (evaluation)(evaluation) (evaluation) Example 8 0.05 Ω(⊚)  10 GΩ(⊚) 1.5 A(◯) Example9 0.05 Ω(⊚)  15 GΩ(⊚) 1.8 A(⊚) Example 10 0.01 Ω(⊚)  15 GΩ(⊚) 2.0 A(⊚)Example 11 0.05 Ω(⊚)  1 GΩ(◯) 1.0 A(◯) Comparative   1 MΩ(X) 100 MΩ(X) —Example 6 Comparative   1 GΩ(X)  1 GΩ(◯) — Example 7 Comparative  100Ω(X)  15 GΩ(⊚) 2.0 A(⊚) Example 8

From Table 3, it was found that both the anisotropic conductive film inthe comparative example 6 in which the spherical Ni powder was containedat a filling factor of 10% by volume and the anisotropic conductive filmin the comparative example 7 in which the spherical metal powder havinga composite structure of the resin particles and the Au coating wascontained at a filling factor of 10% by volume were high in connectingresistance and were inferior in conductive properties in the thicknessdirection of the film. Further, it was also found that the anisotropicconductive film in the comparative example 6 was low in insulatingresistance and therefore, was also inferior in insulating resistance inthe plane direction of the film.

It was found that the anisotropic conductive film in the comparativeexample 8 containing the columnar Cu powder was still high in connectingresistance and was inferior in conductive properties in the thicknessdirection of the film.

On the other hand, it was found that all of the anisotropic conductivefilms in the examples 8 to 11 were low in connecting resistance and weresuperior in conductive properties in the thickness direction of thefilm, and were high in insulating resistance and were superior ininsulating resistance in the plane direction of the film.

From the examples 8 to 10 and the example 11, it was confirmed that inorder to improve the limiting current value of the anisotropicconductive film, the diameter of the chain of the metal powder was in arange exceeding 1 μm and particularly not less than 5 μm.

From the examples 8 and 9 and the example 10, it was confirmed that thesurface of the chain of the metal powder might be coated with a metalsuperior in conductive properties in order to further reduce theconnecting resistance.

1. An anisotropic conductive film characterized in that a metal powderhaving the form of a lot of fine metal particles being linked in a chainshape is contained as a conductive component.
 2. The anisotropicconductive film according to claim 1, characterized in that the chain ofthe metal powder is oriented in the thickness direction of the film. 3.The anisotropic conductive film according to claim 1, characterized inthat the chain-shaped metal powder or each of the metal particlesforming the metal powder is formed of a metal having paramagnetism, analloy of two or more types of metals having paramagnetism, an alloy of ametal having paramagnetism and another metal, or a complex containing ametal having paramagnetism.
 4. The anisotropic conductive film accordingto claim 2, characterized in that the whole or a part of thechain-shaped metal powder or each of the metal particles is formed bybeing deposited in a solution containing one type or two or more typesof metal ions containing ions forming the metal having paramagnetism byreducing the ions to a metal using a reducing agent in the solution. 5.The anisotropic conductive film according to claim 3, characterized inthat the reducing agent is a trivalent titanium compound.
 6. Theanisotropic conductive film according to claim 1, characterized in thata chain-shaped metal powder and a binding agent are respectivelycontained as solid contents, and a filling factor represented by theratio of the amount of the metal powder to the total amount of the solidcontents is 0.05 to 20% by volume.
 7. The anisotropic conductive filmaccording to claim 1, characterized in that used as the metal powder isone having the form of a lot of fine metal particles being linked in astraight-chain shape or a needle shape.
 8. The anisotropic conductivefilm according to claim 1, characterized in that the length of the chainof the metal powder is less than the distance between adjacentelectrodes, composing a connecting portion, conductively connected byusing the anisotropic conductive film.
 9. The anisotropic conductivefilm according to claim 8, characterized in that the diameter of thechain of the metal powder is not more than 1 μm.
 10. The anisotropicconductive film according to claim 9, characterized in that the particlediameter of each of the metal particles is not more than 400 nm.
 11. Theanisotropic conductive film according to claim 8, characterized in thatthe ratio L/D of the length L to the diameter D of the chain of themetal powder is not less than
 3. 12. The anisotropic conductive filmaccording to claim 8, characterized in that the chain-shaped metalpowder is formed of a complex of a chain formed of a metal havingparamagnetism, an alloy of two or more types of metals havingparamagnetism, an alloy of a metal having paramagnetism and anothermetal, or a complex containing a metal having paramagnetism and at leastone metal, with which a surface of the chain is coated, selected from agroup consisting of Cu, Rb, Rh, Pd, Ag, Re, Pt, and Au.
 13. Theanisotropic conductive film according to claim 2, characterized in thatthe diameter of the chain of the metal powder exceeds 1 μm and is notmore than 20 μm.
 14. The anisotropic conductive film according to claim13, characterized in that a chain-shaped metal powder and a bindingagent are respectively contained as solid contents, and a filling factorrepresented by the ratio of the amount of the metal powder to the totalamount of the solid contents is 0.05 to 5% by volume.
 15. Theanisotropic conductive film according to claim 13, characterized in thatthe chain-shaped metal powder is formed of a complex of a chain formedof a metal having paramagnetism, an alloy of two or more types of metalshaving paramagnetism, an alloy of a metal having paramagnetism andanother metal, or a complex containing a metal having paramagnetism andat least one metal, with which a surface of the chain is coated,selected from a group consisting of Cu, Rb, Rh, Pd, Ag, Re, Pt, and Au.16. A method of producing the anisotropic conductive film according toclaim 2, characterized by comprising the steps of applying a compositematerial, having fluidity, containing a chain-shaped metal powder formedof a metal at least a part of which has paramagnetism and a bindingagent on a base to which a magnetic field is applied in a directioncrossing a surface of the base, to orient the chain of the metal powderin the composite material in the thickness direction of the film alongthe direction of the magnetic field, and solidifying or curing thecomposite material to fix the orientation of the chain.
 17. The methodof producing the anisotropic conductive film according to claim 2,characterized by comprising the steps of spraying a chain-shaped metalpowder formed of a metal at least a part of which has paramagnetism on abase to which a magnetic field is applied in a direction crossing asurface of the base, to orient the chain of the metal powder in thedirection of the magnetic field, and applying thereon a coating agent,having fluidity, containing a binding agent, and solidifying or curingthe coating agent to fix the orientation of the chain.